A New Haplotype in the Wheat Fungal Pathogen .

The necrotrophic effector ToxA is a well-studied virulence factor produced by several fungal necrotrophs. Initially cloned from the wheat tan spot pathogen in 1996, was found almost a decade later in another fungal pathogen, and its sister species, . In 2018, ToxA was detected in a third wheat fungal pathogenic species, , which causes spot blotch disease. However, unlike the case with and , the ToxA in has only been investigated in recent years. In this report, five Australian isolates were assessed for the presence of ToxA. Four isolates were found to contain ToxA. While one isolate harbored the previously reported haplotype sequence (, three isolates contain a different haplotype, designated herein as , which has a nonsynonymous mutation resulting in an amino acid change of glycine to arginine at position 168. Both ToxA isoforms, when heterologously expressed in exhibited the classic ToxA necrosis-inducing activity on ToxA-sensitive cultivars. Preliminary analysis of the isolates in Australian wheat cultivars showed that isolates with , or displayed various degrees of virulence, with the most aggressive isolates observed for those producing ToxA. Differences in spot blotch disease severity between and cultivars were observed; however, this was not limited to the ToxA-producing isolates. The overall results suggest that the virulence of the Australian isolates is diverse, with the significance of ToxA- interactions depending on individual isolates.